Ok.
so looking at barriers:
the U.K. literacy rate is 99%. Which is good. But there are people who leave school unable to read. I worked in a secondary school that was the local hub for students with disabilities and every year there were two or three students who left school not able to read. In most cases this was due to disability - Down’s syndrome or similar - although we did have traveller kids who left unable to read because they’d been to so many primary schools they just fell through the gaps.
I believe the traveller community are generally in favour of their kids learning to read and write these days and so most traveler kids do go to primary school but it’s rare for them to continue on to secondary.
then you have situations where mum and dad might be literate but in polish or Romanian and have very limited English - I’ve done plenty of parents evenings where the student has translated both ways.
more generally about 1 in 6 of the population has low functional literacy
https://literacytrust.org.uk/parents-and-families/adult-literacy/
which means that they are literate but at a 9-11 year old reading level.
people who have this level of literacy may well struggle to follow recipes and instructions that they are unfamiliar with.
as a maths teacher, problems with numeracy are also very common.
for example, in the maths national curriculum we explicitly teach how to scale recipes - so if a recipe says it makes enough for 4, calculating the ingredients for if you want enough for 2, or for 8 or 6.
these questions are on the gcse at foundation level and probably about a third of the students really, really struggle with them. They can’t remember how many grams in a kilogram, they don’t know what ml is, etc etc.
Jamie Oliver back in 2008 did a show and a cookbook where he taught people some simple recipes - curry, chilli, etc and got them to pass it on, because he was trying to teach both cooking skills and healthy eating to people who have never seen either.
https://en.wikipedia.org/wiki/Jamie%27s_Ministry_of_Food